slr, grace and swarm gravity field determination and

Astronomical Institute University of Bern

ILRS Workshop Canberra, 05 November 2018

SLR, GRACE and SWARM gravity field determination and combination

Ulrich Meyer1, Krzysztof Sosnica2, Florian Andritsch1, Rolf Dach1, Adrian Jäggi1, Daniel König3 and

Daniela Thaller3

1Astronomical Institute, University of Bern, Switzerland

2Institute of Geodesy and Geoinformatics,Wroclaw University of Environmental and Life Sciences, Poland

3Bundesamt für Kartographie und Geodäsie, Frankfurt, Germany


Contents

⚫ Monthly mass variations in Greenland:

▪ SLR

▪ GRACE

▪ SWARM

⚫ Interpretation:

▪ Spatial resolution

▪ Spectral leakage

⚫ Combination of normal equations:

▪ SWARM + SLR

⚫ Summary and Outlook

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Ice melt in Greenland from SLR

• LAGEOS 1+2: 30 d solutions based on 10 d arcs.• SLR-LEOS (Beacon-C, Ajisai, Starlete, Stella, Larets,

Lares): 30 d solutions based on 1 d arcs.• Gravity field: 5 x 5 + C61 and S61; C50 constrained.• A priori gravity: static 7 y GRACE (AIUB-APR).• A priori orbits: LAGEOS own predictions, LEOS CPF

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Ice melt in Greenland from GRACE

• GRACE GPS+K-band: monthly 90 x 90 gravity field solutions, truncated at degree / order 6.

• Degree 2 excluded.• Degree 1 fixed to 0.• No filter applied.

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Ice melt in Greenland from SWARM

• SWARM GPS: monthly 70 x 70 gravity field solutions, truncated at degree / order 6.

• Degree 2 excluded.• Degree 1 fixed to 0.• No filter applied.

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Spatial resolution and leakage

• The truncation of a spherical harmonic expansion leads to signal leakage.

• Sensitivity for monthly mass variations:• GRACE : 60-90• SWARM: 12-20• SLR: 6-10

• With knowledge about the original mass distribution leakage can be corrected by scaling.

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Spatial resolution and leakage

• Common filters (e.g. Gauss 300km ) lead to drastic leakage even for GRACE.

• All signal above degree 60, and significant signal above degree 30 is attenuated!

• In case of SLR no filter is applied.

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Ice mass change: Greenland Coast

• SLR and GRACE provide consistent mass trends when truncated at the same degree / order.

• By scaling, the original amount of mass loss can be recovered almost completely (but not the spatial detail).

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Ice mass change: Greenland Inland

• Details at small spatial scales are lost. A separation between Greenland coast and inland is not possible with SLR.

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Combination of NEQs: SWARM + 0.01 * SLR

Contribution analysis per SH

coefficient.

Mean contribution per degree.

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coefficient.


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Combination of NEQs: SWARM + SLR


coefficient.


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C20

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• LAGEOS + SLR-LEOs: 30 d C20 values


C20

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• LAGEOS + SLR-LEOs: 30 d C20 values• GRACE: monthly C20 values, strong correlation with

accelerometer temperature


C20

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• LAGEOS + SLR-LEOs: 30 d C20 values.• GRACE: monthly C20 values, strong correlation with

accelerometer temperature.• SWARM: monthly C20 values (no accelerometers

used for signal separation).


C20

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used for signal separation).• SLR + SWARM: C20 dominated by SLR


C20

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used for signal separation).• SLR + SWARM: C20 dominated by SLR• Reference CSR: monthly C20 values for GRACE


Summary and Outlook

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⚫ Truncated to the same spherical harmonic resolution the three space geodetic techniques SLR, high-low-SST (GPS) and low-low-SST (K-band) provide comparable ice mass trends.

⚫ Taking spectral leakage into account the low resolution SLR mass trends are in agreement with high resolution GRACE results.

⚫ Best SLR + SWARM combination results are achieved with equal weighting.

slr, grace and swarm gravity field determination and

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